The present invention relates to an electron microscope for inspecting dimension and shape of a pattern formed on a wafer.
The shape and dimension of a pattern formed on a wafer and those of a photomask pattern are measured and evaluated using an evaluation tool so as to judge the pass/fail. In the measurement of a critical dimension (which, hereinafter, will be referred to as “CD”) in particular, a scanning electron microscope (hereinafter, referred to as “SEM”) equipped with a length-measuring function is generally used.
Also, in accompaniment with microminiaturization and complication of semiconductor integrated circuits in recent years, an optical proximity correction (hereinafter, referred to as “OPC”) has been getting more and more applied to a photomask pattern. Here, the photomask pattern is used when the pattern of a semiconductor integrated circuit is transferred onto a wafer by a microlithography tool. With respect to the pattern transferred onto the wafer by using the OPC-equipped photomask like this, the length-measuring SEM is requested to exhibit an enough resolving power appropriate thereto. Simultaneously, in some cases, it is requested to measure the CD at a larger number of points.
In association with the measurement at a large number of points like this, a lot of proposals have been made concerning technologies for enhancing inspection efficiency by the length-measuring SEM by using CAD (computer aided design) data for determination of the measurement positions and measurement condition of the pattern. For example, as disclosed in JP-A-2003-188074 and the like, pattern image data on the wafer obtained by the length-measuring SEM is compared with the CAD data at the time of pattern design, then displaying differences in dimension and shape therebetween.
In the pattern formation of a semiconductor integrated circuit, it is requested to form the design pattern on the wafer with a desired dimension accuracy. Ensuring the desired dimension accuracy of the pattern on the wafer, however, is becoming increasingly difficult because of the following various causes: Complication of the photomask pattern in accompaniment with the OPC, dimension accuracy of the photomask, and further, stability of the fabrication process. Moreover, the difficulty in the pattern formation has become even more serious because of an increase in pattern data capacity due to the microminiaturization.
On account of this, in order to enhance a reliability in the pattern formation, in addition to the measurement of a representative pattern on the wafer made earlier, there exists a necessity for evaluating and managing the CD such that a full coverage will be made regarding points which are highly likely to give rise to a problem in the pattern dimension from the side of the OPC. However, even if abnormalities of the CD or shape in the pattern have been found out in this way, events which are conceivable as causes for the abnormalities cover a fairly broad range, such as inappropriateness of the OPC, the CD or shape of the photomask, and the fabrication process. Consequently, a task for investigating the complicated causes necessitates tremendous amount of time and labor.